This invention concerns a power unit for an automotive vehicle and an automotive vehicle including such a power unit.
The reduction of fuel consumption of automotive vehicles, in particular trucks, is a major issue for the sustainability of road transport and is a vital element for the competitiveness of trucks manufacturers. A majority of trucks is fitted with a turbocharged diesel engine that runs, on the one hand, the driving wheels through a transmission and, on the other hand, auxiliary equipments, such as a lighting system or a window actuator. Some of these auxiliary equipments are usually fed by an electrical network whose electrical power is produced by an alternator driven by the internal combustion engine of the truck. In order to obtain fuel economies when running an automotive vehicle, one can consider recovering energy which would otherwise be wasted. Known techniques can limit a fraction of the energy losses. This concerns hybrid systems where braking energy is recovered through electrical power storage. In so-called “hybrid electric vehicles” or “HEVs”, one uses a combination of an internal combustion engine with one or several electrical machines and some storage means such as batteries. EP-A-O 366 536 teaches the use of a turbine located in an exhaust line of an internal combustion engine, downstream of a turbocharger, in order to drive an electrical generator which loads a battery. A mechanical pump is also driven by this turbine, in order to load a reservoir of fluid under pressure. No power can be added to the power delivered by the engine. FIG. 1 shows the general layout of a mechanical turbo compound system which comprises an internal combustion engine 11 equipped with a turbo charger 17. A turbine 192 is installed in an exhaust line of engine 11 and coupled, via a hydraulic torque converter 20 and a gear train 13, to the crankshaft 111 of engine 11. Power transmission within converter 20 takes place by friction, which induces high energy losses. Moreover, the speed ratio of the output shaft 193 of turbine 192 and crankshaft 111 is fixed, so that it is not possible to keep items 192 and 111 at rotation speeds corresponding to optimized working conditions for each of them.
According to an aspect of the present invention, a new power unit is provided for an automotive vehicle which enables an efficient energy recovery including when the automotive vehicles run with a stabilized speed, with a great versatility of the conditions of use of the power unit.
The invention concerns, according to an aspect thereof, a power unit for an automotive vehicle, this unit including an internal combustion engine, an electric machine electrically connected to electrical power storage means, a turbocharger comprising a first turbine located in an exhaust line of the engine and a second turbine located in an exhaust line of the engine and drivingly connected to the electric machine. This power unit is characterized in that it further includes a power transmission set having a first input/output connected to the second turbine and a second input/output connected to a crankshaft of the internal combustion engine, whereas the power transmission set has an adjustable speed reduction ratio between its first and second inputs/outputs.
Thanks to an aspect of the invention, energy recovery takes place via the second turbine and the associated power transmission set, whose reduction ratio can be adjusted to optimize the working conditions of both the second turbine and the crankshaft. The power transmission set does not transfer energy by friction, unlike a hydraulic torque converter, which implies that energy losses can be low. The recovered energy can be used either electrically or mechanically, depending on the actual setting of the power transmission set. In particular, the energy recovered by the second turbine can be directed towards the electric machine and/or towards the crankshaft of the internal combustion engine.
According to further aspects of the invention, such a power unit might incorporate one or several of the following features:
According to a first embodiment of the invention, the transmission set comprises a pulley and a belt type continuously variable transmission set (CVT set). The continuously variable power transmission set includes advantageously two bi-conical pulleys connected by a belt, whereas the second turbine and the electric machine are connected to two parts of the same pulley whose relative position can be modified in order to adjust the speed reduction ratio of said transmission set and whereas the crankshaft is connected to the other pulley.
According to another embodiment of the invention, the transmission set is a triple input/output power transmission set having its third input/output connected to the electric machine. Such a transmission set comprises advantageously an epicyclic gear train. According to several embodiments of the invention, the part of the gear train which is coupled to the crankshaft of the engine is its sun, its ring or its satellite-carrier. Similarly, the part of the gear train which is coupled to the turbine can be its sun, its ring or its satellite carrier. The electric machine can work as a generator or as a motor, depending on the working conditions of the power unit.
The unit can include another electric machine electrically connected to the electrical power storage means and coupled to the crankshaft independently of the triple input/output transmission set. The unit can include another electric machine electrically connected to the electrical power storage means and mechanically coupled to the second turbine and to the first input/output of the power transmission set.
The unit can include another electric machine electrically connected to the electrical power storage means and mechanically coupled to a turbine and a compressor of the turbocharger.
The electric machines are connected to the electrical power storage means via a power control unit which is also connected to electrical loads on the vehicle.
Both electric machines can work as a generator or as a motor, depending on the working conditions of the power unit.
The other electric machine can deliver, when it works as a motor, a maximum power which is higher than the maximum power which can be delivered by the electric machine connected to the second input/output of the transmission set. In other words, the other electric machine has a higher power capacity than the electric machine connected to the transmission set.
The second turbine is located in the same exhaust line and downstream of the first turbine.
The invention also concerns an automotive vehicle, in particular a truck, which includes a power unit as mentioned here above. Such a vehicle is more efficient to run than known HEVs.